Advice on how to approach scene involving zooming down to atomic scale?
You will have to blend two shots together. Its most likely impossible to get the geometric level of detail at the atomic scale that will work for a macro shot. I would model the scene with the ruler, with some textures etc.

Then add some procedural textures for pits, scratches, etc. That way we can continue to zoom in without becoming pixellated.

Next model a completely different scene that is molecular in scale and have a zoom animation in both scenes that match up. Once your first scene gets close enough, start blending into the second screen. You could use the compositor, or maybe just a plane in scene 2 that has a texture of the rendered video from scene 1. As you get close in on scene 2, adjust the transparency of that image plane.

Good luck!